Donegild

(3 syl.). The wicked mother of Alla, King of Northumberland.
Hating Cunstance because she was a Christian, she put her on a raft
with her infant son, and turned her adrift. When Alla returned from
Scotland and discovered this cruelty of his mother, he put her to
death. (Chaucer: Man of Lawes Tale.)

The tradition of St. Mungo resembles the Man of Lawes Tale in
many respects.